Examples of such currently-used apparatus include an X-ray CT apparatus. The X-ray CT apparatus includes a radiation source and a detector disposed horizontally so as to face to each other, and a stage between the radiation source and the detector. An inspection object is placed on the stage, and the stage is rotated around a rotation axis, whereby projection images are captured from various angles. Then, the captured projection images are reconstructed to obtain a three-dimensional image such as a tomographic image.
Such an X-ray CT apparatus sometimes requires an increased magnification rate upon inspection of an inspection object having an extremely minute configuration, such as BGA and wires, through tomography. To increase the magnification rate, the radiation source has to be moved close to the inspection object. However, the following drawback may arise when a radiation source 103 faces to a detector 104 horizontally, and an inspection object W is large in a plane direction, as illustrated by chain double-dashed lines in FIG. 1. That is, if the radiation source 103 is moved close to an inspection object W, interference may occur between the radiation source 103 and the inspection object W or between the radiation source 103 and a stage 102. Accordingly, the magnification rate cannot be increased so largely. Then, tomography (Planar Computed Tomography: PCT) has been known as illustrated by solid lines in FIG. 1. That is, the radiation source 103 and the detector 104 are disposed obliquely relative to a plane orthogonal to a rotation axis R for suppressing interference to the inspection object W.
Moreover, a method as illustrated in FIG. 2A other than that in FIG. 1 implements the PCT. See, for example, Japanese Unexamined Patent Publications No. 2010-002221A and 2006-162335A as well as Japanese Patent No. 3694833. Specifically, a radiation source 103 is fixedly disposed for emitting X-rays upward around the rotation axis R in a widespread manner. Tomography is conducted by translating a stage 102 supporting an inspection object W placed thereon around the rotation axis R in circular orbit and rotating a detector 104 around the rotation axis R in synchronization with the movement of the stage 102.
FIG. 2B illustrates a plan view of the stage 102 in FIG. 2A. Stage drive units 137 and 147 are each disposed adjacent to one edge of the stage 102 in FIG. 2B for driving the stage 102. Guiding units 135 and 145 such as guide rails are each disposed on both edges of the stage 102 facing to each other. The stage 102 has an imaging area surrounded with the stage drive units 137 and 147 and the guiding units 135 and 145. The imaging area is hollow with a certain space. See, for example, Japanese Unexamined Patent Publications No. 2008-292383A and 2004-223647A. Such a configuration is intended to prevent an object with low radiolucency from entering into the imaging area and preventing physical interference between the radiation source 103 and the stage drive units 137 and 147.
The apparatus illustrated in FIG. 2A includes drive systems each having the detector 104 and the stage 102 individually. As a result, obtaining an ideal scanning orbit for tomography requires high-accurate positioning as well as a mechanism and control for synchronization of the driving systems. Accordingly, the apparatus becomes expensive. Then, another method has been suggested as following. That is, even when some positional variation exists between actual and ideal scanning orbits, calibration is performed with a calibration phantom to calculate a geometrical positional deviation from the ideal scanning orbit and store the positional deviation as a parameter for correcting the positional deviation upon image reconstruction. See, for example, Japanese Patent No. 4415762.
On the other hand, inspection using projection images has been conventionally performed with a typical X-ray fluoroscopy apparatus. When such an apparatus inspects an inspection object with an extremely minute configuration such as BGA or wires, radiography through oblique emission of X-rays or a high magnification rate is sometimes required. In such a case, a tracking function has been suggested that performs tracking while an attention point of a sample is maintained at the center of the field of view in a fluoroscopy image even with a variation in inclination of X-rays or magnification rate. See, for example, Japanese Patent Publication No. 2004-156927A.